Modelling the temperature effect on bimodally distributed life times

Data on the temperature and humidity relationships of Tetranychus desertorum Banks were reinvestigated to develop a model that describes the dependency between the time course of the adultsʹ age-specific survival rates, on the one hand, and the temperature, on the other. The experimental data ascertained by Nickel (1960, Hilgardia, 30(2): 41–100) differ from other results, because they exhibit marked bimodally distributed life times at the extremes of temperature. The bimodality vanishes at mild temperatures. The observed bimodality results from the fact that the population used in the experiments is divided into two supopulations with different relationships to the environmental conditions. vironment-dependent division of individuals into subpopulations is important for at least three aspects. The first aspect concerns the management of insect populations, the second one concerns the model development and the third one the design of the experiments. If the individuals split into subpopulations, a different population dynamic will result, which will influence the choice of appropriate management methods. With respect to the model development, mixed life time distribution functions are to be used to simulate the observed bimodality. The parameter estimation of these models requires a sufficient amount of data.